I'm writing 'Rails 4 in Action.'
Last night, I took a big step forward in my writing career: I'll be building upon the work Ryan Bigg was doing to take "Rails 3 in Action" and move it to Rails 4. I signed the contract a few weeks ago, but last night I actually did the first bit of editing, and successfully got everything through the system.
Here's the early access edition link, where you can check out what I'm doing. Of course, Rails 4 isn't actually out yet, but since I'm on the Rails team, I already keep abreast of changes daily. I'll be doing a first pass to take the book from 3.2 to edge over the next few weeks, and then keeping it current until the actual release of Rails 4.
Of course, updating the content is much easier than writing it in the first place. Thanks for all of your hard work on previous editions, Yehuda and Ryan!